Thermal inkjet hardcopy devices such as printers, graphics plotters, facsimile machines and copiers have gained wide acceptance. These hardcopy devices are described by W. J. Lloyd and H. T. Taub in “Ink Jet Devices,” Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. The basics of this technology are further disclosed in various articles in several editions of the Hewlett-Packard Journal [Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994)], incorporated herein by reference. Inkjet hardcopy devices produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes the media.
An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes “dot locations”, “dot positions”, or pixels”. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Inkjet hardcopy devices print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more print cartridges each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
The typical inkjet printhead (i.e., the silicon substrate, structures built on the substrate, and connections to the substrate) uses liquid ink (i.e., dissolved colorants or pigments dispersed in a solvent). It has an array of precisely formed orifices or nozzles attached to a printhead substrate that incorporates an array of ink ejection chambers which receive liquid ink from the ink reservoir. Each chamber is located opposite the nozzle so ink can collect between it and the nozzle. The ejection of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements. Properly sequencing the operation of each nozzle causes either to eject ink or to refrain from ejecting ink according to the output of the controlling microprocessor to cause characters or images to be printed upon the media as the printhead moves past the media or the media moves past the printhead.
Color inkjet hardcopy devices commonly employ a plurality of print cartridges, usually two to four, mounted in the printer cartridge to produce a full spectrum of colors. In a printer with four cartridges, each print cartridge can contain a different color ink, with the commonly used base colors being cyan, magenta, yellow, and black. In a printer with two cartridges, one cartridge can contain black ink with the other cartridge being a tri-compartment cartridge containing the base color cyan, magenta and yellow inks, or alternatively, two dual-compartment cartridges may be used to contain the four color inks. In addition, two tri-compartment cartridges may be used to contain six base color inks, for example, black, cyan, magenta, yellow, light cyan and light magenta. Further, other combinations can be employed depending on the number of different base color inks to be used.
The base colors are produced on the media by depositing a drop of the required color onto a dot location, while secondary or shaded colors are formed by depositing multiple drops of different base color inks onto the same dot location, with the overprinting of two or more base colors producing the secondary colors according to well established optical principles.
For many applications, such as personal computer printers and fax machines, the ink reservoir has been incorporated into the pen body such that when the pen runs out of ink, the entire pen, including the printhead, is replaced.
However, for other hardcopy high volume printing applications, such as large format plotting of engineering drawings, color posters and the like, there is a requirement for the use of much larger volumes of ink than can be contained within the replaceable pens. Therefore, various off-board ink reservoir systems have been developed recently which provide an external stationary ink supply connected to the scanning cartridge via a tube. The external ink supply is typically known as an “off-axis,” “off-board,” or “off-carriage” ink supply.
There is a trend to use inkjet printing in new specialized printing systems which are very different systems compared to desk-top printers and facsimile machines, or from large format plotters. These specialized printing systems include applications, such as postal printing, postal franking, label printing and bar code printing. Currently, there are no means to design a specialized printing system without a substantial engineering effort.
In typical inkjet printers the inkjet print cartridges containing the nozzles are scanned or moved repeatedly across the width of the medium to be printed upon. During this movement across the medium, each of the nozzles is caused either to eject ink or to refrain from ejecting ink according to the program output of the controlling microprocessor. Each completed scan or movement across the medium can print a swath approximately as wide as the number of nozzles arranged in a column of the ink cartridge multiplied times the distance between nozzle centers. After each such completed movement or swath the medium is moved or advanced forward the width of the swath, and the ink cartridge begins the next swath.
In inkjet printers the print cartridges need to be periodically serviced. In a scanning carriage printer, a service station is normally located in the scan direction past the edge of the media, since because the scan direction motion is required for printing, it is natural to expand that motion and locate the service station in that direction out of the print zone. Accordingly, when servicing is required, the print cartridges move past the edge of the medium to the location of the service station for servicing.
In printing systems which use stationary print cartridges for printing (such as for example, ticket, tag, label and mail printing), there is no scan direction motion because the print cartridges remain in a fixed or stationary position during printing. In addition, in typical stationary printhead printing systems there may be media movement and drive system mechanisms which make accessing the print cartridges difficult. Because of these difficulties, many stationary printhead printing systems do not use service stations. The disadvantage of this approach is that the performance of the printhead decreases as nozzles become dried and ink residue builds up on the printhead orifice plate. Accordingly, periodically it is necessary for an operator technician to manually remove the print cartridges and manually clean the orifice plates. This type of operation is not well controlled and depends on user know-how and consistent execution and exposes the printheads to damage if done incorrectly.
Accordingly, there is a need for a solution to the servicing of print cartridges in specialty printing systems which often use print cartridges which are stationary during the printing operation with only the media moving through the print zone. With stationary printhead printers, a new means for making the print cartridges accessible to service station components is required.